Techniques and Tutorials

Curdling Butter and Sugar with Eggs

Prompted by a comment, I’ve been researching what happens when creamed butter and sugar become curdled with the addition of the eggs when making a cake. There are four things to think about here: why does it happen, does it matter if it happens, what can I do to prevent it happening, and if it does happen, can I fix it? I’ll take them in turn.

Why does creamed butter and sugar curdle when eggs are added?

It helps first to understand the point of creaming and what’s happening when this is done. Creaming, according to Paula Figoni, incorporates air bubbles into plastic fats (ie into the butter). The tiny fat crystals surround the air bubbles and keep them from popping. These air bubbles then help to leaven the cake.

When eggs are added to creamed butter and sugar they act as an emulsifier (if added correctly). They stabilize the creamed mixture, and then help it to blend with the other ingredients. What you’re creating here by creaming and then adding egg is a water-in-oil emulsion. There’s a great and detailed explanation of this at the excellent Using Mainly Spoons blog, with useful pictures. They wisely suggest thinking of the process of adding eggs to butter and sugar as like the stage of adding oil to eggs when making mayonnaise. I’ll just quote them as they explain it so well:

when you start to add the eggs, you are aiming for little droplets of the water from the eggs, suspended through the fat-and-sugar mixture that is already there. At some point, the liquid from the eggs can overwhelm the amount of fat, causing the bubbles of water to all join up and become the main part of the mixture – the continuous phase, as it’s called.

To prevent this happening, you need to ensure that the fat and sugar are able to hold as much liquid as possible – which means soft, but not melted. You also need to add the egg very gradually, so that it doesn’t overwhelm the mixture. This is the same principle as adding oil to mayonnaise – go slowly and incorporate each bit before you add some more.

Crafty Baking have even more detail on what’s going on when you’re creating the butter / sugar / egg emulsion.

Does it matter if my butter, sugar and egg mixture is curdled?

I’ve read and heard that it doesn’t matter, but I’m inclined to believe that it does. Figoni suggests that

A poorly emulsified batter bakes into a cake that may not rise properly and that has a coarser crumb.

Delia Smith, doyenne of British cookery, agrees, explaining that the curdling causes the mixture to ‘break up’ and this means that

some of the air incorporated at the creaming stage will escape and the finished cake will be slightly heavier.

Crafty Baking are a little more doomy, but I think they’re referring to really bad curdling when they say the result could be

a baked cake that is grainy or flat in texture, dry and flavorless, look uneven and may even sink.

How can I prevent curdling?

Curdling by adding eggs can happen for two reasons. First, the eggs are too cold, and this breaks the emulsion of butter and sugar. Second, the eggs are added too quickly, again breaking the emulsion. The result looks like little lumps of butter and sugar in liquid. Adding mix can also curdle a mixture. There are a few things, therefore, that you can do to avoid curdling:

Tip 1: Use eggs that are the same temperature as the butter and sugar (between 18 and 21C ideally for everything).

That said, Crafty Baking says that in fact you can use cold eggs if you’re using a stand mixer, and that even if it curdles a little, it will sort itself out as you beat, just go slowly. This matches up with my experience.

Tip 2: Gently whisk the egg yolk and white together before adding

Tip 3: Add slowly, in a steady stream.

If you’ve ever made mayonnaise, it’s the same approach (for the same reasons – maintaining the emulsion). The liquid in the eggs doesn’t naturally want to mix with the fat in the butter, but if you go slow, it will be fine.

Tip 4: Add milk and flour alternately. Don’t dump in all the milk, mix and then add all the flour.

Once the eggs are safely in, beat for a minute or two and the mixture will become even more smooth and fluffy, full of lovely, tiny bubbles ready to expand in the oven and make your cake light and delicious.

If all this fails, take heart from Delia, who says ‘the cake won’t be as light but it’s not a disaster’. And as the next section explains, all is not lost – it can be remedied.

What can I do if my mixture has curdled?

Add a little flour and beat again. This can help bind the mixture back together. Or, once you begin to add the flour and milk, it will sort itself out naturally.




Creaming Butter and Sugar

I explored this when I undertook my Victoria Sponge project, and here I give a fuller account of the role of creaming and how to approach it. I’m indebted as always to some great sources to helped me learn about this, particularly  Crafty Baking, which has a long, detailed discussion of creaming theory that I won’t repeat here, and the inimitable Joe Pastry. I’ve also discovered recently that the wonderful Poires au Chocolat blog has a similar post all about creaming, which I found very informative and would highly recommend. The basic principle I’ve gleaned from reading these and other sources is that by creaming butter and sugar you are trying to aerate the mix. The sugar crystals cut into the butter, forming small air cells or bubbles. When the batter is heated, these bubbles expand and lighten the cake. So naturally, for a light cake, you want more bubbles and ones that expand appropriately. It’s important to note that leaveners (such as baking powder) don’t create more bubbles when they release carbon dioxide nor does any steam produced when the cake batter heats up. Instead, the carbon dioxide and steam cause the existing bubbles to increase in size as they fill up the air cells (the bubbles). The cells expand until the batter sets and this determines the cake structure. Therefore, it seems logical that beating the butter and sugar until super fluffy would give you more bubbles, and that the more bubbles, the lighter and fluffier the cake. Not surprisingly, then, most recipes will tell you to aim for fluffy, pale-coloured butter/sugar mix, using softened butter and beating for at least 5 minutes. Many recipes and bakers subscribe to this view, for example here, here and here.

Crafty Baking disagrees on the need for huge amounts of beating, and even argues that butter shouldn’t be too soft as it tends to melt too much when beaten (due to the heat from the friction of beating). They suggest aiming for below room temperature, and after everything has been combined, the mix should be what they say is the optimum temperature for cake batter – 20 – 22C. There is sense to the Crafty Baking view. Too few bubbles means a heavy dense cake or one with a coarse structure (as the small number of air cells will take up more of the carbon dioxide and steam), and just the right amount means a light, tender cake, but you can have too many. Paula Figoni explains in How Baking Works that too many of these ‘seed’ (ie initial) air cells mean that:

cell walls become overstretched, thin and weak. During baking, these thin cell walls stretch further and collapse… the baked goods will have poor volume.

In my Victoria Sponge project, I compared the Craft Baking approach with the standard fluffy creaming approach, and found that for me at least, it didn’t make a huge difference. So my preference is to stick with going for full fluffiness, but it’s obviusly a matter of personal preference and Crafty Baking’s approach works too.

If this is the way you want to go, then there are some key things to take account of for success:

Tip 1: Butter must be soft but not too soft

It needs to be pliable, but you don’t want it to get oily. One is usually told to use butter that’s ‘room temperature’ but I live in the UK by a river, so ‘room temperature’ is about 15C in my house, which is way too cold. I think you want it at about 20C. How to achieve this? Emma at Poires has a method that also works well of making laminated dough (and Richard Bertinet takes this approach too), where you beat the butter with a rolling pin between baking paper while still cool. This makes it plastic (ie bendy) but not too warm (ie it doesn’t get oily). Mary Berry, on the other hand, says put the cold butter into lukewarm water for 10 minutes (by lukewarm, she means ‘baby’s bath temperature’, which is about 37C). Both approaches are good if your house isn’t warm enough for room temperature butter to be soft enough to beat. The one big no-no is microwaving. Or at least, beware… microwaving is, I think, a bit of a dark art here. You can successfully soften butter, but because things warm from the inside out, often the inside is a bit melty by the time the outside is just right. And you can get hot spots. If you really want to do it that way, go slow and steady — better to go for a minute or so on ‘defrost’ or ‘low’, than bursts at ‘high’ I find. King Arthur Flour has some nice pictures of how microwaving can go just so wrong (as well as more useful information on creaming). As they explain, butter that’s too soft won’t be able to capture air bubbles, while if it’s too hard, it can’t exapnd and become aerated as the sugar crystals ‘punch holes in it’.

Tip 2: Beat butter first then add sugar slowly

You can bosh them together (I do below), but I think if you have time, start with butter first then add sugar slowly. Joe certainly favours this approach.

Tip 3: It takes longer than you might think. About 8-10 minutes for me with my mixer (but time isn’t determinative).

However, that’s in my cold house without beating super-fast (because I don’t want the butter to heat up and become melted or greasy – see more below). Here’s how mine looked over time, photos at 0, 1, 3 and 10 minutes:

Pre-creaming (obviously)


After 1 minute of creaming


After 3 minutes of creaming


After 10 minutes of creaming


So the final, big question is how do you know when it’s done? There are various hallmarks:

Sign no. 1: It’s more pale in colour, like ivory, rather than yellow

This perhaps isn’t that helpful. As Stella Parks writes at Serious Eats

Watching butter and sugar as they’re creamed together is about as dramatic as sorting through shades of beige at Sherwin-Williams. “Snow White” sugar and “Daffodil” butter lighten to “Antique Ivory,” then “Elegant Ecru,” shifting colors so subtly that some part of you screams, “It’s all the same!”

So she coloured her’s blue! There are some great photos here of the results, which I completely love.

Sign no. 2: It won’t look grainy (but it won’t be perfectly smooth either – you’ll be able to feel some grains if you rub some between your fingers). This is a bit sugar-dependent, so normal sugar will result in a grainier mix than caster and brown sugars.

Sign no. 3: It’s fluffy and light

For me, this takes nearly 10 minutes, but I don’t beat it crazy fast, and my house is cold. Interestingly, others find it takes only about 3 minutes. And it is possible to overdo it. There’s a great post here at The Cake Blog about this, where they compared the results of beating for 3 and 6 minutes (both mixes were fluffy). They reported:

The three-minute cake has a softer, tenderer text than the one-minute cake and baked perfectly flat. The six-minute cake was slightly coarser and just a bit cottony when compared to the three minute cake. So, it appears that you can under or over cream your butter and sugar…If you under mix, the sugar granules stay course and not enough fine air particles are incorporated into the cake batter to make it light and fluffy. When the sugar and butter are properly creamed the mixture becomes lighter and less dense…When the butter and sugar are over mixed the butter becomes excessively soft and less capable of holding air pockets. The sugar also starts to dissolve, making the mixture more liquid and less able to hold onto fine air cells. The resultant cake becomes coarser as the larger and less numerous air pockets converge.

Really interesting results there, echoing, in fact, the points made by Crafy Baking about making the butter too fluffy and hence too soft. I’d conclude, then, that you need it to be fluffy but not at the expense of the butter getting too warm. For Crafty Baking, the ideal temperature for the final butter/sugar is around 17.5 – 18.5C (63-65F), and as butter starts to melt at 20C (68F), there’s clearly a line to walk here — fluffy, but not melty. I think you get a sense of this by eye and feel, but if you’re going for perfection, perhaps it’s a good time to get the instant read thermometer out! The main thing is, watch it like a hawk, get it fluffy but don’t let it get melty or greasy looking. If that happens, stop and let it cool a little before going any further.

Who would have thought there was so much to say just about creaming butter and sugar!

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